The MPO connectors are the angle-polished (APC) type which provide minimal reflection of the optical signal for optimal signal integrity.
Multimode Fiber Cable with MPO/APC Connectors
Detail of the MPO/APC Connector
Transceivers have alignment pins for precise positioning of the cable connector against the optical beams. The fiber cable has alignment holes matching the transceiver’s pins.
MPO Connector with Alignment Holes and Positioning Key
Optical Receptacle and Lane Assignment (transceiver, front view)
Reference: IEC specification IEC 61754-7.